Defining Dosimetric Reference Levels in Computed Tomography Spectral Scanning

Defining Dosimetric Reference Levels in Computed Tomography Spectral Scanning

Spectral computed tomography or dual-energy CT imaging can overcome the limitations of conventional CT in differentiating between two materials with equivalent total attenuation. It can generate several types of images, such as virtual monochromatic images, which improve the contrast-to-noise ratio for low energy levels and reduce artifacts for high energy levels. It also allows for quantitative image analysis and thus better characterization of lesions and tissues through material mapping (e.g., iodinated contrast agent mapping). This technique is increasingly used in routine clinical practice thanks to improvements in image flow management and technological advances. It also involves exposing patients to ionizing radiation, as with conventional CT but, unlike conventional CT scans, for which dosimetric reference levels (RLs) are defined for the most common examinations in France (RL decree dated 2019), there are currently no dosimetric reference levels for examinations performed using this technique. Yet RLs are an important and effective tools for optimizing patient exposure to ionizing radiation. Several articles were published between 2012 and 2017 when the first dual-energy scanners arrived in clinics. However, the results presented in these studies are now far removed from recent practices, as they do not take into account the latest technological developments used in dual-energy scanners, which reduce X-ray doses.

The main objective of the study is to define dosimetric reference levels for the most commonly performed spectral computed tomography examinations in France.

Spectral computed tomography (CT) (or dual-energy CT) imaging can overcome the limitations of conventional CT in differentiating between two materials with equivalent total attenuation. It can generate several types of images, such as virtual monochromatic images, which improve the contrast-to-noise ratio for low energy levels and reduce artifacts for high energy levels. It also allows for quantitative image analysis and thus better characterization of lesions and tissues through material mapping (e.g., iodinated contrast agent mapping). This technique is increasingly used in routine clinical practice thanks to improvements in image flow management and technological advances. It also involves exposing patients to ionizing radiation, as with conventional CT.

However, unlike conventional CT scans, for which dosimetric reference levels (RLs) are defined for the most common examinations in France (RL decree dated 2019), there are currently no dosimetric reference levels for examinations performed using this technique. Yet the RL is an important and effective tool in optimizing patient exposure to ionizing radiation. In fact, a number of articles were published between 2012 and 2017, when the first dual-energy scanners arrived in clinics. However, the results presented in these studies are now far removed from recent practices, as they do not take into account the latest technological developments used in dual-energy scanners, which reduce X-ray doses.

The main objective of the study is to define dosimetric reference levels for the most frequently performed spectral computed tomography examinations in France:

1. Chest CT for pulmonary embolism
2. Chest CT for other indications
3. Coronary CT with contrast injection and retrospective gating
4. Coronary CT with contrast injection and prospective gating
5. Cranial CT with contrast injection
6. Supra-aortic trunk CT
7. Neck and ear,nose and throat sphere CT with contrast injection
8. Oncological abdomen-pelvis CT scan
9. Abdomen-pelvis CT scan to check for kidney stones
10. Abdomen-pelvis CT scan for non-oncological purposes and to check for kidney stones
11. Oncological chest-abdomen-pelvis CT scan
12. Non-oncological chest-abdomen-pelvis CT scan
13. Oncological chest-abdomen CT scan
14. Non-oncological chest-abdomen CT scan
15. Lower limb angiography
16. Cervical spine CT scan
17. Thoracic spine CT scan
18. Lumbar spine CT scan
19. Pelvis CT scan,
20. Extremities CT scan

The secondary objectives of the study are to evaluate, for each examination performed:

1. the impact of the spectral acquisition/detection technique on the dose delivered to patients.
2. the impact of patients' BMI on the dose delivered to patients.
3. the impact of reconstruction algorithms on the dose delivered to patients.

Inclusion Criteria:

• Adult male/female patient (≥ 18 years old)
• Body Mass Index (BMI) between 18 and 35 kg/m²
• Patients who underwent a spectral CT scan between January 1, 2023, and August 31, 2024, as part of their treatment.

Exclusion Criteria:

- Pregnant women